In gas turbine applications, superalloys, MCrAlY bond coatings, and overlay coatings often contain elements such as aluminum or chromium for oxidation and corrosion resistance. One or more of these elements form a thermally grown oxide (TGO) layer on the surface which acts as a barrier to further oxidation and corrosion. Over time, alloying elements like Ti, W, Ta or Hf diffuse up from the substrate and into the thermally grown oxide layer. Such impurities degrade the thermally grown oxide layer and reduce its protective ability. There can also be a significant loss of aluminum via diffusion from the bond coat into the substrate, thereby reducing the aluminum reservoir required to maintain the protective layer.
There is a need in the art for thermal barrier coating systems and overlay coating systems that reduce interdiffusion of elements between the substrate and the bond coat in order to increase the life of the systems. The present invention is directed to these. as well as other, important ends.